HEAT
Heat capacity
Heat is an agent that produces the sensation of warmth. When
an object is heated, its molecule begins to move faster. Heat always flows from
a hotter body to a colder body.
The temperature of a
substance is the degree of its hotness or coldness. Three temperature scales commonly used to measure temperature are the Celsius scale, the Fahrenheit scale, and the Kelvin scale. The SI unit of temperature is Kelvin (K).
Specific heat
Specific heat of a substance is the
ratio of the heat required to raise 1 gm of it through 10C to the
heat required to raise 1 gm of water through 10C.
The thermal capacity
of a body is the quantity of heat regulated to raise the temperature of the
body through 10C.
Latent Heat
When a solid is
heated its temperature remains constant. So the heat supplied at the melting
point of a solid is used not to raise its temperature but to convert the
solid to a liquid state. This heat is called the Latent heat.
The latent heat of
fusion of a solid is the quantity of heat required to convert one gm of the
solid at its normal melting point into a liquid without rising temperature. The latent heat of the fusion of ice is the quantity of heat required to convert one gm
of ice at 00C into water.
Latent heat of vaporization
Latent heat of
vaporization of a liquid is the quantity of heat required to convert on gm of
the liquid at its boiling point into vapour without rising temperature.
The latent heat of
steam is the quantity of heat given out by one gram of steam at 1000C
when converted into water at 1000C.
Vapor pressure
The space above
a liquid in the enclosure always contains the vapour of the liquid. The pressure
exerted by this vapour on the liquid surface is called vapour pressure.
Transmission of heat
Conduction is the process by which heat is transmitted from
the hot to the cold end of a body without the actual movement of the particles
of the body.
For instance, when one end of a metal rod is heated, the heat is transmitted through the
successive layers to the other end. In this case, heat is communicated through
the successive layers of the rod without the movement of the layers.
The substances
which readily transmit heat by conduction through them are called good
conductors. Substances that do not readily transmit heat by conduction are
called poor conductors. Usually, metals are good conductors like copper and
aluminium but non-metals are poor heat conductors like glass and wood.
Convention
Convention is the process by which heat is transmitted through
a medium by the actual movement of the heated particles of the medium. Convection
takes place only in liquids and gases.
For instance, if
water in a beaker is heated, the bottom layer receives heat, becomes less
dense, and rises. The colder, denser water at the top sinks down. This in
turn gets heated and rises up. Thus the whole water gets heated. This process
of transmission of heat is called convection.
Radiation
Radiation is the
process by which heat is transmitted from one place to another without the help
of any material medium.
For instance,
the sun’s heat reaches the earth after travelling empty space and then the
atmosphere. The atmosphere is not heated due to the radiant heat passing
through it. This process of transmission of heat is called radiation.
Tags
science